The present invention relates generally to gas turbine engines, and more specifically, to a turbine blade having an extensible tail.
The desirability of providing fuel efficient gas turbines is well known. Clearly, the fuel efficiency of a gas turbine directly impacts operating costs. In the case of gas turbine engines used in aircraft, the benefits of providing fuel efficient engines are reduced operating costs, increased engine performance and increased range, since the aircraft is capable of flying farther on the same amount of fuel.
Generally, gas turbine engines include, at a minimum, a compressor section, a combustor, and at least one turbine section. During operation, ambient air enters the compressor section where it is pressurized and subsequently discharged to the combustor to be mixed with fuel and ignited. The hot gasses thus generated are directed into the turbine section whereupon some of the energy therein is extracted by the turbine blades. After passing through the turbine section, the gasses are exhausted from the engine. In this manner, a significant amount of thrust for propulsion of the aircraft is generated. Moreover, the turbine blades are designed to impart a rotational force to the rotor upon which they are attached. This rotational force is utilized to impart the requisite energy to the compressor section to continuously compress the ambient air in order to maintain the operation of the gas turbine engine.
Gas turbine engine configurations can vary. For example, a fan section can be placed upstream of the compressor section. The turbine can have more than one rotor shaft. The turbine can include several rows of turbine blades of increasing size in order to extract more energy from the combustion gas divided into high pressure and low pressure sections. In this way, gas turbine configurations are varied, depending on the desired performance and operational characteristics expected to be encountered in service.
As can be appreciated, the operating environment that a gas turbine engine used on aircraft is exposed to varies markedly. For example, the airflow through the engine varies with the throttle position selected by the pilot as well as altitude. Thus, while gas turbine designs are chosen carefully in order to maximize operational output, the final design is chosen in light of the entire range of operating conditions expected to be encountered by the aircraft in flight. As expected, this can result in operational compromises that while not catastrophically impacting the operation of the aircraft, are not without the need for improvement.
A number of attempts to improve the performance of gas turbines by varying nozzle area have been made to date. Many are directed to varying the nozzle inlet area in the turbine section. See, for example, U.S. Pat. No. 3,966,352 to White et al. See also, U.S. Pat. No. 5,806,302 describing a variable fan exhaust nozzle for tailoring the exit throat area of the fan air stream to specific conditions encountered in flight.
While not unsuccessful, the various prior art attempts have need for improvement. More specifically, it has been determined that the configuration of the turbine blades themselves sometimes contribute to a degradation in performance. This is because the turbine blades are designed for extracting energy from the combustion gasses over the entire range of expected operating conditions. As a result, the configuration of the blade thus represents a degree of compromise in order to provide the best performance overall. More specifically, turbine blade performance may actually be reduced in certain, transient operating conditions experienced by the aircraft in favor of overall performance. This reduction in performance is due, at least in part, to the development of zones of undesirable flow characteristics along the surface of the turbine blade. These undesirable flow zones can arise from the negative effects of unpredictable transition zones existing between areas of laminar and turbulent flow, or they can arise from the separation of boundary layer flow giving rise to separation zones or bubbles. In either case, these undesirable flow zones can become quite large, increasing fuel consumption as well as lowering engine performance.
A need exists therefore for an improved turbine blade exhibiting desirable performance characteristics throughout the operating range of the turbine engine.
It is therefore a primary object of the present invention to provide a turbine blade displaying optimal performance characteristics throughout the expected operating conditions of the turbine engine.
It is another object of the present invention to provide a turbine blade having an extensible tail to control the extent of undesirable flow zones across the blade.
It is still another object of the present invention to provide a turbine blade displaying smaller undesirable flow zones during turbine operation.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.